1. Field of the Invention
The present invention relates to an electrode structure of capacitor, and more particularly to an electrode structure of capacitor using materials of high dielectric constant.
2. Description of the Background Art
Studies on dielectric of high dielectric constant have been conventionally made in order to increase capacitance of a capacitor in highly-integrated DRAM. For example, barium strontium titanate ((BabSr1-b)TiO3:0 less than b less than 1, hereinafter referred to as xe2x80x9cBSTxe2x80x9d) is introduced in Japanese Patent Application Laid Open Gazette No. 10-256503.
FIG. 20 is a cross section showing an exemplary structure of DRAM. In an upper surface of a semiconductor substrate 31, an isolation oxide film 33 and an isolation impurity layer 35 are formed, and in a region of the upper surface of the semiconductor substrate 31 sectioned by these constituents, three impurity layers 25 are formed. The center impurity layer 25 is shared by a pair of MIS transistors 30 and the right and left impurity layers 25 are in contact with contact plugs 26a. 
Each MIS transistor 30 has a gate insulating film 21, a gate electrode 23 formed on the gate insulating film 21 and an insulating film 27 covering the gate electrode 23. Between a pair of insulating films 27, a bit line 37 connected to the center impurity layer 25 is provided. The insulating films 27 and the bit line 37 are covered with an interlayer insulating film 24a while the contact plugs 26a penetrate the interlayer insulating film 24a to come into contact with barrier layers 61a. Upper and side surfaces of the barrier layer 61a are covered with lower electrodes 62a and 63a mainly made of platinum, which are further covered with a high-permittivity layer 64 (i.e., dielectric layer with high permittivity) made of BST. The high-permittivity layer 64 is covered with an upper electrode 81 mainly made of platinum, and the upper electrode 81 is further covered with a conductive film 10. The conductive film 10 is covered with an interlayer insulating film 41.
The lower electrodes 62a and 63a, the upper electrode 81 and the high-permittivity layer 64 constitute a capacitor, and one electrode of the capacitor is connected to the bit line 37 through the barrier layer 61a, the contact plug 26a and the transistor 30.
On the other hand, the interlayer insulating film 41 is locally removed, and a layered structure consisting of a barrier layer 42 and an aluminum wire 43 is connected to the conductive layer 10. Therefore, the other electrode of the capacitor is connected to the aluminum wire 43 through the upper electrode 81, the conductive layer 10 and the barrier layer 42.
FIG. 21 is a cross section showing constituents of the conductive layer 10 and connection between the conductive layer 10 and the layered structure of the barrier layer 42 and the aluminum wire 43. The conductive layer 10 has a layered structure consisting of a barrier layer 10a, a stopper layer 10b and an adhesion layer 10c in this order from the near side of the upper electrode 81. In some cases, the barrier layer 42 penetrates the adhesion layer 10c as shown in this figure due to overetching in anisotropic etching on the interlayer insulating film 41 to provide a trench for placing the aluminum wire 43. The barrier layer 10a is made of, e.g., TiN to suppress a reaction in a heat treatment on the aluminum wire 43 and the upper electrode 81. Further, the stopper layer 10b is made of PtSi since it works as a sacrifice reacting film when the aluminum wire 43 and the upper electrode 81 are reacted in the heat treatment. The stopper layer 10b also works to suppress the overetching when the interlayer insulating film 41 is anisotropically etched to provide a trench for placing the aluminum wire 43. The adhesion layer 10c is formed to improve adhesion between the conductive film 10 and the interlayer insulating film 41 and, for example, made of TiN when the interlayer insulating film 41 is a silicon oxide. The structure of FIG. 21 is shown, for example, in Japanese Patent Application Laid Open Gazette No. 10-256503.
In the above structure, however, the capability of the barrier layer 10a as a barrier is not perfect, and a reaction may be caused between the PtSi of the stopper layer 10b and Pt of the upper electrode 81. With such a reaction, the BST may be reduced in an interface between the upper electrode 81 and the high-permittivity layer 64. Further, depositing the conductive film 10 and the upper electrode 81 thereon puts a stress on the high-permittivity layer 64.
The present invention is directed to an electrode structure of capacitor. According to a first aspect of the present invention, the electrode structure of capacitor has a first electrode layer; and a second electrode layer including platinum, silicon and at least one of oxygen and nitrogen, in this order from the side in contact with a dielectric layer of the capacitor.
Preferably, the second electrode layer has a higher composition ratio of at least one of oxygen and nitrogen on the near side from the first electrode layer than on the far side thereof.
According to a second aspect of the present invention, in the electrode structure of the first aspect, the second electrode layer has a double-layered structure, consisting of a third electrode layer located on the near side of the first electrode layer and a fourth electrode layer located on the far side thereof, and the third electrode layer has a higher composition ratio of at least one of oxygen and nitrogen than the fourth electrode layer.
According to a third aspect of the present invention, in the electrode structure of the second aspect, the fourth electrode layer also works as an adhesion layer.
According to a fourth aspect of the present invention, in the electrode structure of any one of the first to third aspects, platinum oxide is used for the first electrode layer.
Preferably, the dielectric layer is made of dielectric oxide.
The present invention is also directed to a capacitor. According to a fifth aspect of the present invention, the capacitor comprises: a dielectric layer; a first electrode layer formed on the dielectric layer; and a second electrode layer formed on the first electrode layer, including platinum, silicon and at least one of oxygen and nitrogen.
Preferably, the second electrode layer has a higher composition ratio of at least one of oxygen and nitrogen on the near side from the first electrode layer than on the far side thereof.
According to a sixth aspect of the present invention, in the capacitor of the fifth aspect, the second electrode layer has a double-layered structure, consisting of a third electrode layer located on the near side of the first electrode layer and a fourth electrode layer located on the far side thereof, and the third electrode layer has a higher composition ratio of at least one of oxygen and nitrogen than the fourth electrode layer.
According to a seventh aspect of the present invention, in the capacitor of the sixth aspect, the fourth electrode layer also works as an adhesion layer.
According to an eighth aspect of the present invention, in the capacitor of any one of the fifth to seventh aspects, platinum oxide is used for the first electrode layer.
Preferably, the dielectric layer is made of dielectric oxide.
The present invention is further directed to a DRAM. According to a ninth aspect of the present invention, the DRAM comprises: a capacitor having a dielectric layer, a first electrode layer formed on the dielectric layer, and a second electrode layer formed on the first electrode layer, including platinum, silicon and at least one of oxygen and nitrogen.
Preferably, the second electrode layer has a higher composition ratio of at least one of oxygen and nitrogen on the near side from the first electrode layer than on the far side thereof.
According to a tenth aspect of the present invention, in the DRAM of the ninth aspect, the second electrode layer has a double-layered structure, consisting of a third electrode layer located on the near side of the first electrode layer and a fourth electrode layer located on the far side thereof, and the third electrode layer has a higher composition ratio of at least one of oxygen and nitrogen than the fourth electrode layer.
According to an eleventh aspect of the present invention, in the DRAM of tenth aspect, the fourth electrode layer also works as an adhesion layer.
According to a twelfth aspect of the present invention, in the DRAM of any one of the ninth to eleventh aspects, platinum oxide is used for the first electrode layer.
Preferably, the dielectric layer is made of dielectric oxide.
In the electrode structure of capacitor of the first aspect, since the second electrode layer relieves a stress on the dielectric layer, the dielectric characteristics of the dialectic layer can be improved.
In the electrode structure of capacitor of the second aspect, the third electrode layer and the fourth electrode layer each working as a barrier layer can be consecutively formed by sputtering using one target and one chamber.
In the electrode structure of capacitor of the third aspect, since the second electrode layer also works as an adhesion layer, no adhesion layer has to be provided.
In the electrode structure of capacitor of the fourth aspect, since reduction on the dielectric layer is prevented, it is possible to suppress deterioration of the dielectric layer even if an oxide is used for the dielectric layer.
In the capacitor of the fifth aspect, since the second electrode layer relieves a stress on the dielectric layer, the dielectric characteristics of the dialectic layer can be improved.
In the capacitor of the sixth aspect, the third electrode layer and the fourth electrode layer each working as a barrier layer can be consecutively formed by sputtering using one target and one chamber.
In the capacitor of the seventh aspect, since the second electrode layer also works as an adhesion layer, no adhesion layer has to be provided.
In the capacitor of the eighth aspect, since reduction on the dielectric layer is prevented, it is possible to suppress deterioration of the dielectric layer even if an oxide is used for the dielectric layer.
In the DRAM of the ninth aspect, since the second electrode layer relieves a stress on the dielectric layer, the dielectric characteristics of the dialectic layer can be improved.
In the DRAM of the tenth aspect, the third electrode layer and the fourth electrode layer each working as a barrier layer can be consecutively formed by sputtering using one target and one chamber.
In the DRAM of the eleventh aspect, since the second electrode layer also works as an adhesion layer, no adhesion layer has to be provided.
In the DRAM of the twelfth aspect, since reduction on the dielectric layer is prevented, it is possible to suppress deterioration of the dielectric layer even if an oxide is used for the dielectric layer.
With the above reduction and application of stress, there is a possibility of deteriorating the dielectric characteristics of the high-permittivity layer 64. An object of the present invention is to provide an electrode structure of capacitor to reduce the possibility and improve the dielectric characteristics of the high-permittivity layer 64.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.